The invention relates to fluid purifiers, and more particularly to gas purifiers. By way of non-limiting example, the invention relates to in-line gas purifiers used in the semiconductor industry for such purposes as removing contaminants from purging gasses.
There are a number of reasons for providing purging gasses for the semiconductor and other industries. For example, in the semiconductor industry, the high-precision optics of photolithography machines (e.g. stepper machines) and the equally high-precision optics of wafer inspection machines use purging gasses to ensure, among other things, that the optics are immersed in an ultra-clean operating environment.
One form of purging gas is referred to as Clean Dry Air (“CDA”). CDA is sometimes synthesized by mixing highly purified oxygen and nitrogen (“synthetic air”), typically in the same proportion that they are found in natural air. Other forms of purging gas include purified nitrogen. However, even CDA, synthetic air, and purified nitrogen have been known to carry contaminants which can build up or react with, for example, high precision optics.
Lithographic processes are widely used for the production of integrated circuits for electronic devices. Lithographic processes are also useful in a variety of other applications well known to those of skill in the relevant arts. If the radiant energy source is visible or near visible light (e.g. ultraviolet or “UV” light), the process is often referred to as photolithography.
Photolithography machines are typically found in clean rooms. As such, they are often exposed to other processing machines (e.g. etching machines, deposition machines, etc.) which can generate gaseous, liquid, and particulate contaminants in the clean room environment. Photolithography machines are made by such companies as Nikon, Canon, and others.
The photolithographic process uses photo-sensitive chemicals (often referred to as “photoresist”) that, once exposed to a radiant energy source, change in chemical composition. Photoresist is typically coated onto a semiconductor wafer and cured before the semiconductor wafer is inserted into a photolithography machine. The photoresist may then be selectively exposed to the radiant energy source of the photolithography machine, e.g. through a mask, such that the exposed portions of the photoresist undergo a chemical transformation.
Since the optics of the photolithography machine are in close proximity to the photoresist, there is a possibility of generating contaminants from the photoresist and elsewhere during the photolithography process. The optical components are delicate and may be damaged if exposed to impurities that are produced as by-products during the photolithography phase. In particular gaseous impurities can create deposits on the optics, causing aberrations in their transmission properties. Moreover, energy transfer from the radiant energy source to the deposits on the optics may eventually lead to irreversible damage of the optics. This is particularly problematic due to the high cost of high-precision optical assemblies, which can cost many hundreds of thousands of dollars.
As mentioned previously, certain wafer inspection tools also use high-precision optics and employ the use of purging gas. For example, KLA Tencor makes wafer inspection equipment which use high-precision optics. Some wafer inspection equipment use UV or deep ultraviolet (DUV) light to enhance the sensitivity of the wafer inspection equipment. Other wafer inspection tools use other radiant energy sources. The optical components of the wafer inspection tools have contamination risks similar to optical components in lithographic processes.
Three exemplary classes of compounds that are detrimental to the optical components are acids, bases, and hydrocarbons. Examples of impurities that fall into these exemplary classes are SO2 and H2S (acids), NH3 and ammines (bases), and toluene and decane (hydrocarbons). A large number of other substances, whether known or unknown, are categorizable into one or more of the classes by those of ordinary skill in the material and/or chemical sciences.
It may be desirable to develop a technique for purifying a purging gas to prevent or reduce the likelihood that impurities reach optical components, either from the ambient environment or from the purging gas itself. Attempts to address this problem include compressed air purification and filtering.
U.S. Pat. No. 5,607,647 describes an air filtering system for use in a clean environment made by a two-media sequence. The first media is carbon impregnated with sulfuric acid, which is effective to remove basic impurities. (As used herein, a “basic impurity” is an impurity that is a base, and an “acidic impurity” is an impurity that is an acid.) As a consequence of the basic impurities removal, a characteristic volatile compound is released and removed by a second media. Therefore the process described in this patent is a two-step removal process for a single class of contaminants, namely basic impurities. U.S. Pat. No. 5,626,820 describes a similar concept applied to clean room air purification.
U.S. Pub. No. 20030159586 describes a two media purification method in which acidic contaminants are removed by a first media, while removal of other impurities is carried out by a second media. U.S. Pat. No. 6,645,898 describes a “synergistic” effect for compressed air purification obtained by employing a ternary composition made by an electropositive metal, a late transition metal, and a high silica zeolite.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.